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US regulators have upheld a fine on Barclays and four of its traders of $453m (£300m) for allegedly manipulating electricity prices.

Barclays must pay $435m within 30 days, while one trader must pay $15m and three others $1m each.

Barclays must also forgo $34.9m in profits, which will be distributed to low-income aid programmes in Arizona, California, Oregon and Washington.

Barclays said it intended to "vigorously defend this matter".

The fines were first proposed by staff at the Federal Energy Regulatory Commission (FERC) last October, and have now been upheld by the body's board of commissioners.

FERC accused Barclays of manipulating the electricity markets in California and other states from November 2006 to December 2008.

But the bank said in a statement: "We are disappointed by the action that FERC took today. We believe the penalty assessed by the FERC is without basis, and we strongly disagree with the allegations made."

In addition to the company fine, Barclays traders Daniel Brin, Scott Connelly, Karen Levine and Ryan Smith - who are accused of manipulating an index relating to electric energy prices in the western part of the US - were ordered to pay substantial sums.

Mr Connelly must pay $15m, while Mr Brin, Ms Levine and Mr Smith were told they owed $1m each.

Regulators relied on electronic communication between the traders to build their case.

In a series of electronic messages, according to the FERC complaint, the traders boasted of their ability to manipulate markets.

In an email exchange, one of Mr Connelly's colleagues asks: "You going to have fun with the index all month?" and in another, Mr Connelly responds to details of market volatility with: "Crazy - I love it."

One exchange, dubbed the "Friday burrito incident" in the report, is singled out for particular mention.

The FERC alleges that Mr Connelly sought to deliberately misdirect a staff member of the Western Power Trading Forum, who published an energy newsletter called the Friday Burrito.

The FERC alleges that Mr Connelly responded to an article noting unusual patterns of trading with a seemingly innocuous explanation denying manipulation and told the publisher to "embrace the change". Mr Connelly then allowed his response to be published anonymously.

All four traders have left the firm.

This is the latest scandal to rock the bank.

Barclays was fined £290m last year by UK and US regulators for attempting to rig the key Libor interest rate.